The present invention relates to the loading of fuel rods with spherical nuclear fuel.
In recent years it has been discovered that conventional nuclear reaction fuel composed of fuel pellets encased in cladding tubes may lead to the splitting of the cladding tubes thereby releasing radioactive material to the adjacent cooling water. This splitting is due to an interaction between the pellet and cladding. One way of avoiding this problem is to limit the surface interaction between the fuel and cladding. This may be achieved by loading the fuel cladding tubes with nuclear fuel in the shape of spheres. If three different sizes of spheres are used, then appropriate packing of the spheres into the rods will result in a sufficient density of nuclear fuel to be properly used in a nuclear reactor.
One method for loading a fuel rod is to simply drop the spheres into a vertical cladding tube while vibrating the rod to assist in packing. However, this method is not satisfactory for several reasons. The distribution of the particles sizes freely falling from a height of 6 to 12 feet into a cladding tube does not lead to uniform distribution. This method also leads to the trapping of air which requires a longer time to evacuate at the sealing of the tube. In addition, the vibrating packing is extended because of the random loading of the spheres.